Magnetic unit with magnetically positioned pole piece for loudspeakers



July 22, 1952 R. D. cHARLEswoRTl-l 2,604,551

MAGNETIC UNIT WITH MAGNETICALLY POSITIONED POLE PIECE FOR LOUD-SPEAKERS 2 SHEETS-SHEET 1 Filed Aug. 28. 1948 Gttornegs R. D. cHARLEswoRTH 2,604,551 v MAGNETIC UNIT WITH MAGNETICALLY POSITIONED July 22, 1952 POLE PIECE FQR LOUD-SPEAKERS 2 SHEETS-SHEET 2 Filed Aug. 28, 1948 Suunto: ,PFG/MILD Milf/007W attorneys Patented July 22, 1.952

OFFICE'- MAGNETIC UNIT WITH MAGNETICALLY .POSITIONED POLE PIECE FOR LOUD SPEAKERS Reginald Denison Charlesworth, Dee Why, New South Wales, Australia, assignor to Magnavox (Australia) Pty. Ltd., East Sydney, New South Wales, Australia, a corporation of Australia Application August 28, 1948, Serial No. 59,322

In Australia October` 2, 1947 6 Claims.

and has been devised to producefmagnetic units that are complete in themselves and may be manufactured in various sizes and powers and vused or storedfor Vlater usewith particular diaphragm 4units .andA locking means also of independentindividual, construction whereby the units may besecuredto each other in operative relationrso thatthe individual units of a loud speaker may be demounted, inspected, cleaned, replaced or interchangedV without l the use of gauges, jigs, or special or, precision equipment;

Hitherto designs and methods ofassembly of loud speakers of the moving coil type include having at least one member of the magnetic section as an inseparablevor lintegralY part of the diaphragm head assembly-usually held by rivets or the like. This leaves much to be desired with respect to dismantling vthe speaker for cleaning and servicing because in these constructions the magnetic section has to be dismantled piecemeal in order. to gain accessto the voice coil and the magneticv air gap. `'.I'his piecemeal dismantling breaks the magnetic. iiux locked up in the structure and on're-'assemb'ly lthe lost. fluxhas ,to be replaced by re-charging before .the speaker can function again efciently. v Furthermore the reassembly calls for considerable skill even to those well practised in the art. Therefore one of the principal objectslof this invention is to provide a magnetic unit complete in itself and so formed as to be readily detached from a complete loud speaker so that the voice coil and the air gap can be cleaned Without further dismantling and to be accurately re-attached to any suitable diaphragm head assembly without the use of gauges, jigs, or the like.

Another object of this invention is to provide a complete removable magnetic unit for loud speakers in which the relevant parts of the unit are held in correct and secure alignment without the aid of assembly screws, rivets, adhesives o the like usually employed in the art.

A further Object of the invention is to provide a complete detachablev magnetic unit so formed as to be manufactured in various sizes or powers for storage or immediate use and to be 'capable of assembly at will to. anyv suitable diaphragm head unit of the various sizes, thereby giving great flexibility of type and production speed by using units from stock or directly co-relating them on the production lines.

According to this invention I provide a magnetic structure comprising atop plate formed or provided with contiunous or non-continuous steps, ledges, recesses, bosses or the like aspositioning and nesting means' on its upper and lower surfaces; an orifice for providing the outer boundary of an air gap to be formed therein said orifice positioned in strict relation to the said positioning and 'nesting means; aV non-magnetic centering ring,fnestin`g in the under surface `of the top plate and securedthereto by riveting, peening or the like, so that the ring aperture is concentric With the top plate orifice. Thisring aperture is adapted to present a neat sliding fit to a central floating pole piece of magnetic material that projects through the ring aperture' and into the top plate orice'to form vac o'ncen'tric air gap, and a magnet pot encasing said floating pole piece and adapted to nest in positioning and nesting means on the lower face of the top plate.

The upper and lowersurfaces` of the top plate may be provided withv one type of `positioningand nesting means or different types of these means may be used simultaneously on'the different srfaces,

The top plate is of any desired shapeg'siz and thickness, and the steps, ledges, recesses, bosses or the like positioning and nesting means may be formed by extrusion, pressure or other suitable methods. They may be formed, for example, by securing to each surface of the topplateilat metal rings or the like that have continuous or non-continuous peripheral surfaces and So that the steps or the like are, preferably,` at right angles to the top plate and function as automatic positioning and nesting means for applyingldetachable structuresl such as thel lower end 'of a diaphragm assemblyv unit' and the upper end of a magnet pot so ,that they are in correct operative positions. jpi In the preferred method of assembly ofthe magnetic unit the detachabl-e oatingpole piece is, preferably, a magnetisable cylindrical slugand may lcomprise thewhole'of the central pole piece.

tral pole piece is assembled into the pot with the top plate in position it is charged magnetically and the working flux density is so high that the pull on the bottom of the pot is sufficient, in conjunction with the non-magnetic` centering ring, to prevent any undesired movement of theloating slug and its position makes a correct and uniform air gap with the Wall of the top plate orifice. Furthermore the top plate and the, pot are held together magnetically, forming a. cornplete magnetic unit.

In a modified form of the magnetic unit the central pole piece may consist of aY detachable mild steel tip or pole piece that fits at its front end into the non-magnetic centering ring to form an air gap. It is constructed to contact magnetically at its bottom surface with a oating slug of magnetizable material that nests into a recess in the base of the pot said recess providing locating means for the slug and preventing lateral movement of the slug. When this assembly is charged magnetically it is held together as a unit by magnetic force, the mild steel tip being held to the surface of the slug, and together with the non-magnetic ring, prevents any undesirable movement of the mild steel tip and makes an accurate air gap with the. wall of. the top plate orice.

The magnet pot is of known formation and material but may be provided about its upper end with an outwardly projecting metal flange that is adapted to be nested in positioning and nesting means on the under face of the top plate, and, in addition to its magnetic'eiects the flange may., in some forms of construction, function as means associated with locking members for detachably securing the magnetic unit to the diaphragm assembly unit of the loud speaker.

For use with magnet pots of larger than normal size the top plate is correspondingly enlarged and provided with its orifice in correct relation to thepositioning and nesting means on the top plate, the positioning and nesting means are also enlarged to effect secure and detachable locking of the magnetic unit to the diaphragm assembly unit.

In the accompanying drawings which illustrate several forms of construction of my magnetic unit:

Fig` 1 is a central sectional elevation of a top. plate withcentering ring;

Fig. 2 is a plan of the same;

Fig. 3 is a central sectional elevation of a modi fled forml of top plate;

Fig. 4 isa central sectional elevation of a complete magnetic unit;

Fig. 5 is a similar view of a modied form of construction;

Fig. 6 is a top plan of a modified form of top plate; Y

Fig. l is a part sectional elevation on line 'lof Fig. 6;.

Fig. 8 is a section on line 8 8 of Fig. '7.

A top plate I0 is provided with positioning and nesting means in the form of continuous right angled steps I 0A on its upper and lower surfaces, and with an orifice IOB located in relation to the positioning means IDA. An inner step on the under surface of the plate serves to locate and nest a non-magnetic centering ring II formed with an aperture IIA of smaller diameter than that of orifice IIB, but concentric therewith. An Vouter step on the under surface of the plate is adapted to locate and nest a magnet pot I2 (Fig. 4). A step on the upperV surface of the plate is adapted to locate and nest a diaphragm assembly unit, such as those in Figs. l and 5.

In a modified form of top plate (Fig. 3) the upper surface of the plate, inplace of the steps IUA of Fig. 1, is provided with positioning and nesting means in the form of circumferentially spaced bosses I3Ithat function similarly to the steps IDA of Fig. 1. The positioning and nesting means. on the under surface in this form of plate are similar to those of the under surface of Fig. 1.

As illustrated in Fig. 4 a diaphragm assembly unit shown in part elevation has a housing eX- tension member I4 the lower end of which is located and nested by a step IIIA, the voice coil IAA passes concentrcally through the orifice IIIB of plate IQ and air gap IIIB between the plate and central pole piece. The voice coil is spaced from both the plate and the central pole piece. A voice coil former 3.0 is indicated as receiving the voice coil I 4A.

A central pole piece in the. form ofA a cylindrical floating slug I5 of' magnetic material makes a close or tight t with the aperture IIA of centering ring II and at its lower end is held magnetically to the inner bottom surface of the magnet pot I2 when the unit is energised.

In a modified form of assembly as shown in Fig. 5 the voice coil I4A similarly ts Within the orifice IUB of an enlarged'top plate IDC. A pole piece I5A projects at its upper end through the centering ring II and into the orifice IGB in the top plate to form the air gap I4B for the voice coil. The lower end of pole piece IEA makes magnetic contactl with ama'gnetic slug IEB that is nested in a recess "ISC in the-base of the 'enlarged magnet pot IZA. An outer circular ange I6 on the diaphragm housing I'Iis providedwith a series of spaced slots [6A to serve as part locking means when the diaphragm assembly unit 'is locked on the magnetic unit.

In the modified form of top plate (Figs. 6, l and 8) the plate I0 has the orice IBB, and in place of the positioning'and nesting steps IIIA of the earlier figures has positioning and nesting means in the form of spaced'bosses I8 on its upper surface; Ybosses IBA on its lower surface nest the magnetic pot. This pot plate also nests the centering ring II, with aperture IIAV in the step IIIA. Y

The types of positioningand nesting'means illustrated may be replaced in Whole or in part by equivalent means of the type described. y

Having now particularlydescribed and ascertained the nature of thissaid invention, and in what manner the same is to be performed I declare that what I claim is: l

V1. Ina loud speaker of the movingA coil type, a magnetic assembly unit comprising in combination, a top plate with its surfaces broken to form positioning and nesting means and containing Y an air gap orifice accurately located in relation 2. In a-loud speaker of the moving coil type, Ia magnetic assembly unit compriisng in combination, a top plate with its surfaces broken to form positioning and nesting means and containing an air gap orice accurately located in relation to said positioning and nesting means, a nonmagnetic centering ring mounted by the positioning and nesting means on the top plate in concentric relation to the air gap orifice, a magnet pot engaging the top plate, and a magnetic slug contained within and movable laterally of said pot and positioned therein by means of said centering ring through which the slug extends.

3. In a loud speaker of the moving coil type,

-a'magnetic assembly unit comprising a top plate with its surfaces broken to form positioning and nesting means and containing an air gap orifice located ln relation to the positioning and nesting means. a non-magnetic centering ring mounted in concentric relation to the air gap orifice, a magnet pot engaging the lower surface of the top plate and located by positioning and nesting means in the lower surface of said top plate, said pot containing a magnetic slug nested in and held magnetically in the base of the pot, said slug terminating below the surface of the said centering ring and surmounted with a mild steel pole piece terminating within the air gap oriice and to be disposed concentrically therein by the said centering ring to form a concentric air gap and to be held at its base magnetically to the upper surface of the said magnetic slug.

4.- A magnetic assembly unit according to claim 1 in which an air gap is formed by the top plate orifice having a portion of the magnetic slug held in concentric relation with the wall of the orifice, said air gap being accurately located in relation to positioning and nesting means in the said top plate so that the positioning and nesting means may locate and removablyl position a diaphragm assembly unit in such a manner that a voice coil associatedwith the diaphragm unit is located concentrically and in correct operative position in the magnetic air gap.

5. In a loud speaker according to claim 2, a. magnetic top plate in which the positioning and nesting means are in the form of circumferentially spaced bosses.

6. In a loud speaker of the moving coil type according to claim 2, a magnetic unit formed of the magnet pot and slug, the unit being held together in operative relation by its own magnetic force when the slug is energized.

REGINALD DENIS ON CHARLESWORTH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

